The present invention relates to improvements in construction of floating apparatus intended for operating at sea in unsheltered water, for example, of the type normally used for underwater oil drilling operations, for laying pipelines on the sea bed, or as a support for cranes, an industrial plant, the storage of supplies, aircraft landing sites and the like.
For the various uses indicated above, it is essential that there should be little rocking or other movement of the apparatus in response to the action of the waves. This object is achieved partially in semi-submersible platforms of the type stabilized by pillars. Such apparatus consists basically of two or more submerged hulls from which there emerges a series of pillars on which the actual working platform rests and acts as a base for the corresponding equipment and installations.
When the apparatus is in the operative position, the level of the water extends to approximately half the height of the pillars. The bottom hulls are submerged and provide the buoyancy required for floatability of the apparatus. The working platform, which will hereinafter be referred to as the top hull, is above the sea level at a height sufficient to avoid the effect of the waves. With this arrangement, the pillar assembly provides the apparatus with the stability required to avoid overturning.
Owing to the large size of such apparatus, its steel structure is very heavy and expensive. The large dimensions also give rise to constructional problems in the shipyard. Nevertheless, to obtain good seagoing conditions in rough seas and to enable very heavy equipment and sufficient consumable material to be housed in the top hull without adversely affecting the stability of the apparatus, the stabilizer columns must necessarily be as far apart as possible. This normally means a general increase in dimensions and hence increased cost and increased difficulties with respect to construction.